All for One

Wake-Up Call

Now that you have an image, you can launch a virtual machine directly:

qemu -hda windows.img -cdrom /dev/cdrom U
   -boot once=d -m 512M

Some distributions, including OpenSUSE call this program qemu-kvm, but the parameters stay the same (see the "Double Trouble" box):

qemu-kvm -hda windows.img U
   -cdrom /dev/cdrom -boot once=d -m 512M

Qemu mounts the image that you created as the first hard disk (-hda) then mounts the physical CD-ROM drive (which uses a device called /dev/cdrom in the sample). Qemu immediately boots from the CD-ROM (-boot once=d; to boot from the first hard disk, you would need once=c). Then Qemu opens a new window in which all the screen output from the virtual machine is displayed. If you do not want to use the physical CD drive, you can integrate an ISO image instead :

qemu -hda windows.img U
   -cdrom /home/tim/debian.iso U
   -boot once=d -m 512M

This process provides a fairly simple way to try out a new distribution without needing to waste a CD.

By default, Qemu gives virtual machines just 128MB of RAM – state of art operating systems will just laugh at this. To assign more RAM, you need the -m parameter; the example assigns 512MB. You will need at least 1GB Windows 7. You should avoid assigning all of your physical memory resources to the virtual machines. Doing so would leave the host system and Qemu without enough air to breathe. The amount of RAM needed depends on the distribution. Ubuntu and openSUSE will need at least 512MB.

Figure 4: Qemu was unable to access the KVM services here. You can normally ignore the message about the missing romfile as it relates to booting off the network.

Figure 5: As the lsmod command shows, both KVM kernel modules (kvm and kvm_intel) have loaded correctly.

Modulo

Qemu output shows important status messages to the terminal window (Figure 4). In Figure 5, the output is complaining about a lack of support from KVM. In a case like this, you should first check whether the driver is loaded correctly. The driver comprises the kvm.ko kernel module, which provides some basic functionality to Qemu, and a processor specific module, kvm-intel.ko or kvm-amd.ko. Issuing the following command should provide your current combination:

lsmod | egrep '(kvm)'

Otherwise, the following commands will let you load the module manually:

sudo modprobe kvm
sudo modprobe kvm-intel

or for an AMD model:

sudo modprobe kvm
sudo modprobe kvm-amd

If this approach doesn't work, the messages in your kernel log will provide more information about the problem. The KVM FAQ [5] is also useful if you need help, and questions are answered on the KVM mailing list or the forum [6].

Grabbers

You can install the operating system in the normal way on the virtual machine. Clicking the window with the mouse captures the mouse cursor and lets you use it on the guest system. Pressing Ctrl+Alt gives the mouse back. Some Linux distributions detect Qemu and do without mouse cursor integration. You can then use Qemu like any normal application on the host system.

Besides a Cirrus CLGD 5446 PCI graphics adapter, Qemu emulates older standard hardware for which nearly any operating system will have matching drivers. However, you can't run 3D applications, especially not games.

If the desired operating system refuses to launch, you can try switching off KVM by executing qemu with the -no-kvm parameter. You can also try replacing the virtual graphics adapter with a simple model by adding a -std-vga switch. For Windows XP, you also need to disable the power saver function by adding -no-acpi.

Figure 6: The Qemu Monitor lets you control your virtual machines. The "info block" command outputs details of the drives.